Combustion air control shutter



1970 P. w. PILLSBURY ETAL 3,490,230

COMBUSTION AIR CONTROL SHUTTER Filed March 22, 1968 FIG. 2

FIG. 4 INVENTORS PAUL W P/LLSBURY JEFFREY K. 3075/? BYMM G. Ahab ifATTORNEY AGE/VT United States Patent US. Cl. 6039.65 2 Claims ABSTRACTOF THE DISCLOSURE A turbojet combustor is provided with scoop ductsmounted on a rotary shutter to control injection of additional air tothe burner dome. At low altitude, when smoke is objectionable, the pilotcauses rotation of the shutter. The scoop ducts are tilted to produce aswirling air pattern directed at the fuel spray.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION Field of the invention The invention relatesto turbojet engines and com bustors and, more particularly, to effortsto reduce smoke and resulting pollution of the air produced by suchengines.

Description of the prior art In the turbojet engines known to the priorart, a considerable amount of smoke is produced at the airfuel ratioswhich are required for satisfactory operation of the engine, especiallyat the high throttle settings utilized in low altitude operation fortake-off and landing. In order to obtain favorable characteristics ofthe engine in regard to resistance of the tendency to blowout the flameof the engine and to enable relighting of the engine at high altitudesafter such a blow-out, it has been necessary to provide the engine witha rich mixture. Unfortunately, such a mixture produces a substantialamount of smoke in operation, especially at the lower altitudes. Withthe increasing concern about air pollution, it has become desirable tolimit or reduce the quantities of such contaminates which are releasedto the atmosphere, particularly at the lower altitudes where such smokecontributes most to air pollution. This is especially true since thenumber of such engines installed in commercial and military aircraft issteadily increasing. It is known that such smoke could be substantiallyreduced by operating the engine with higher air-fuel ratio. As discussedabove, however, constant use of such a ratio is not practicable due tothe adverse elfects produced on the altitude relight and blow-out limitscharacteristics. The present invention solves this dilemma by providingscoop ducts which can be opened or shut by means of a rotary shutter onthe burner dome so that additional air may be injected when low smokecharacteristics are desired but may be shut-01f during normal operationso as to retain favorable altitude relight and blow-out limits.

Other means are known to the prior art for injecting additional air intoa turbojet engine, but these means are located in other parts of theengine and perform different functions than that of the presentinvention. For example, additional air ducts have been provided to mixcool air with combustion products leaving the combustion chamber inorder to cool the mixture which will flow over the turbine blades. Also,regulatory means 3,490,230 Patented Jan. 20, 1970 have been provided toautomatically provide a correct air-fuel ratio. Additional ducts havealso been known to provide supplementary air to an after-burner. Thedistinctions of the present invention over such prior art constructionswill be discussed more fully below.

SUMMARY OF THE INVENTION The present invention involves the modificationof the well-known turbojet configuration in which a plurality ofcombustors are arranged in a circumferential configuration about theturbine shaft between the turbine and the compressor. These combustorsare conventionally provided with an upstream fuel nozzle contained in aburner can-dome. Downstream, the burner-can is preforated to allow airto mix with the sprayed fuel. The modification of the present inventioninvolves the provision of additional air ducts in the burner can-domeand the control of passage of air through the ducts by a rotary shutteroperable by the pilot. The placement of the additional ducts is suchthat air exiting from the ducts is directed at or near the base of thefuel spray and the ducts may be arranged so as to produce a swirling airpattern. The combination of the swirling air pattern and the directionof the auxiliary air ducts provides for exceptionally completecombustion of the fuel, which results in a great decrease of smokeproducts caused by incomplete combustion.

An object of the present invention is to provide means for reducing theamount of smoke in the exhaust of a gas turbine engine.

Another object of the present invention is to provide means for reducinggas turbine exhaust smoke which ca be operated at will.

A further object of the present invention is to provide means forselectively effecting a substantial change in the air-fuel ratio in theturbine combustor.

Still another object of the present invention is to provide means forinjecting additional air into the burner dome of a turbine combustor andto direct the additional air so as to insure relatively completecombustion of the fuel.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a side elevation of a turbineengine iricorporating the combustor air control shutter of the presentinvention, with certain parts broken away to better show the relevantinterior construction of the engine;

FIG. 2 is a longitudinal section of the upper combustor shown in FIG. 1;

FIG. 3 is an end view of a combustor incorporating a shutter of thepresent invention, looking from the left in FIG. 2, and showing the airinlet scoops in closed position; and

FIG. 4 is an end view of a combustor as shown in FIG. 3 with the shuttermoved so that the air inlet scoops are in open position.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings,wherein like reference characters designate like or corresponding partsthroughout the several views, there is shown in FIG. 1, whichillustrates a preferred embodiment, a turbojet engine 11 comprising acompressor 12 and turbine 13. A plurality of combustors 14 are arrangedcircumferentially about a shaft 16 which connects the turbine andcompressor assemblies. As is shown more particularly in FIG. 2, the

combustor 14 consists of a burner can 17 and a plurality of burnershrouds 18. The burner shrouds are provided with air inlet holes 19. Theburner can dome area 21 is provided with a central opening 22 containingan air swirler 23 which surrounds a fuel nozzle 24. Fuel is supplied tothe nozzle through fuel line 26. Air coming from the compressor (fromthe left in FIG. 2) is directed through the air swirler to be thoroughlymixed with fuel from the fuel spray nozzle. Additional air is admittedto the combustor through air inlet holes 19. In the combustor known tothe prior art, the amount of air admitted by the air swirler end 23 andthe air inlet holes 19 creates the necessarily rich air-fuel ratiorequired in order to maintain altitude relight and blow-out limitscharacteristics.

The modification of the present invention enables the normal richmixture to be temporarily leaned when it is desired to reduce the amountof smoke emanating from the engine. In the present invention, primaryair inlet holes 27 are provided in the burner-dome 21. Admission of airthrough the primary air inlet holes 27 is controlled by a rotary shutterplate 28 which further includes primary air inlet scoops 29 directingair to openings in the shutter plate. The rotary shutter 28 is adaptedto be rtated between the position shown in FIG. 4 where the primary airinlet scoops are aligned with the primary air inlet holes in theburner-dome and the position in FIG. 3 where the primary air inletscoops are not aligned with the primary air inlet holes, therebycutting-off the flow of air through these holes.

Rotation of the rotary shutter between the positions of FIG. 3 and FIG.4 is accomplished by the movement of actuator rod 31 attached to lug 32on the rotary shutter. Rod 31 may be actuated by the pilot through anyconventional actuating means such as by hydraulic or pneumaticservo-cylinders or by solenoids, electric motors, etc.

It can be seen from FIG. 2 that the primary air inlet holes 27 perform afunction which is different in kind from the prior art air inlet holes19. The primary function of the latter holes is to mix cool air with thecombustion products in the combustor so as to reduce the temperature ofthe gas mixture flowing over the turbine assembly. The primary air inletscoops and holes, however, perform the function of providing a radicallydifferent air-fuel mixture ratio for the novel purpose of eliminatingexcessive smoke from the engine exhaust.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings.

What is claimed is:

1. A turbine combustor comprising:

a burner can including a dome area;

a fuel injector fixed in the dome area of said burner can and coaxialwith said burner can;

an air swirler formed in said dome area of said burner can andconcentrically disposed about said fuel injector;

a plurality of air inlet openings formed in said dome area arranged in acircular pattern about said air swirler;

a plate rotatably mounted on the exterior of said dome area and normallypositioned to preclude flow of air through said openings;

a plurality of air scoops fixed on said plate in a circular patterncomplementary to the pattern of said air inlet openings; and

means for selectively moving said plate to bring said air scoops intoregistry with said air inlet openings whereby the additional airadmitted to said burner can will vary the air-fuel ratio provided bysaid fuel injector and said air swirler to lean out the mixture andeliminate excessive smoke from the exhaust.

2. The turbine combustor of claim 1 wherein said air scoops are tiltedwith respect to the longitudinal axis of the burner can for directingthe additional air in a swirling pattern about said axis.

References Cited UNITED STATES PATENTS 1,733,792 10/1929 Good 6O 39.232,227,666 l/l94l Noack 39.23 XR 2,560,207 7/1951 Berggren et al 6039.652,770,096 ll/1956 Fox 6039.29 2,907,171 10/1959 Lysholm 6039.652,960,823 11/1960 FOX.

MARK M. NEWMAN, Primary Examiner A. D. HERRMANN, Assistant Examiner US.Cl. X.R. 43 l352

